1. Field of the Invention
The present invention relates to electrical machines in general and, in particular, to processor-based electrical machines that can be serviced while performing its assigned tasks.
2. Prior Art
Because of increasing dependency on electrical machines in general, and processor-based machines in particular, there is a need for processor-based machines (hereafter called computers) which can be serviced while performing regular functions. A typical computer includes a motherboard and /or backplane with a plurality of slots. The slots are the receptacles for adapters or cards which can be used to expand the capacity and functionality of the computer. Occasionally, adapters become defective and have to be replaced. To provide uninterrupted service, the computer has to be fully operational during removal or insertion of the adapters. In addition, the removal and/or insertion must not have deleterious results on the computer operations.
A technique termed "hot plugging", "hot swap", or variations thereof enables the insertion and/or removal of adapters while the computer is operational. Even though hot plugging is a desirable goal, if not done properly, it can cause problems which over time adversely affect the operability of the computer system. A likely problem is pitting of the metal used on the connecting pins located on the adapter and the connector. A main cause of pitting is believed to be electrical arcing which occurs at the electrical contacts while interconnection is made or broken. Another problem is electrical noise which can adversely affect the performance of the system. The cause of this noise is believed to be the large change in current over a short period of time (di/dt) at the instance when the connection is made between power pins on the card and the socket. This problem is particularly severe when hot-plugging an adapter card with a large amount of decoupling capacitance. Finally, the large surge of current is likely to cause voltage transients onto the computer system backplane. The voltage transients can cause loss of data, incorrect program execution and, in severe situations, damage to delicate hardware components.
The prior art has recognized the need for precautions and have provided system and method which go a long way to minimize some of the problems. The populous prior art solution is the use of "staggered-pins" to sequence power and signals from the host system to the card being hot plugged. In some implementation, additional electrical circuits are used to charge the card capacitance in a controlled way. The "staggered pins" means that the lengths of the pins making the interconnection varies. Usually, the power carrying pins are longer than the signal carrying ones. Consequently, when the card is inserted into the connector, power is established before signaling. Likewise, when the card is removed, the signal pins are disconnected prior to the power pins. One of the problems with this popular solution is that connectors with special pins are required. Another problem is that staggered pins necessitate the use of proprietary adapter design. The cost associated with fabricating and manufacturing connectors with special pins unnecessarily increases the price of the Box. As used in this document, "Box" refers to the system in which the card is plugged.
Another problem with the "staggered pins" arrangement is that the connect/disconnect time is sometimes too short for the system to perform an orderly logical shut down and/or "bring-up" of the adapter. The connect/disconnect time covers the time delay for the long/short power/signal pins on the card to contact/disconnect the power/signal pins on the system to which the adapter is inserted. Usually, the connect/disconnect times, for the "staggered-pins" arrangement, are in the order of milliseconds. Longer times are required for adequate shutdown and/or bring-up of complex adapters. This time may grow even longer as more functions are placed on the adapter.
Consequently, there is a need for a hot-plug system that affords sufficient time to shut down and/or bring-up the functions on the adapter before the adapter is inserted or removed from the system.
A less populous but effective solution uses electrical circuits and switches for coupling the card's power and signal busses to the system's power and signal busses. U.S. Pat. No. 5,473,499, "Hot Pluggable Motherboard Bus Connection Method", by Steven Weir, is an example of the solution. Even though the patent teachings are in the right direction, because the pins in the connector are of the same length rather than staggered, it too has drawbacks which the below invention solves.
One of the drawbacks is that the patent requires a predetermined time delay between connection of the power busses and the signal busses. The predetermined time delay enables the voltages on the card to be stabilized before the signal busses are connected. It appears as if operator's intervention is required to set the predetermined time which may be different for different systems and even in the same system, may have to change as components age. Due to the likelihood of human error, there is a need to provide a fully automated system which does not require human intervention, other than to insert/remove the card.